Concerning the polymerization of propylene, Ziegler-Natta catalysts can be made from or contain a solid catalyst component, constituted by a magnesium dihalide on which are supported a titanium compound and an internal electron donor compound, used in combination with an Al-alkyl compound. When higher crystallinity of the polymer is desired, an external donor can be used to obtain higher isotacticity. Internal donors can be constituted by the esters of phthalic acid. The phthalates can be used as internal donors in combination with alkylalkoxysilanes as external donors. This catalyst system gives good performances in terms of activity, isotacticity and xylene insolubility.
The use of this catalyst system has raised health concerns.